AIDS is an immunosuppressive or immunodestructive disease that predisposes subjects to fatal opportunistic infections. Characteristically, AIDS is associated with a progressive depletion of T-cells, especially the helper-inducer subset bearing the OKT.sup.4 surface marker.
Human immunodeficiency virus (HIV) has been reproducibly isolated from patients with AIDS or with the symptoms that frequently precede AIDS. HIV is cytopathic and appears to preferentially infect and destroy T-cells bearing the OKT.sup.4 marker, and it is now generally recognized that HIV is the etiological agent of AIDS.
Since the discovery that HIV is the etiological agent of AIDS, numerous proposals have been made for anti-HIV chemotherapeutic agents that may be effective in treating AIDS sufferers. Thus, for example, U.S. Pat. No. 4,724,232 and European Patent Specification No. 196185 describe 3'-azido-3'-deoxythymidine (which has the approved name zidovudine), its pharmaceutically acceptable derivatives and their use in the treatment of human retrovirus infections including AIDS and associated clinical conditions.
European Patent Publication No. 0206497 relates generally to 2',3'-dideoxypurine nucleosides for use in the treatment of HIV infections and related conditions. In particular this publication discloses 2,6-diaminopurine-9-.beta.-D-2',3'-dideoxyribofuranoside for the treatment of HIV infections.
Another group of viral pathogens of major consequence worldwide are the hepatitis viruses, in particular hepatitis B virus (HBV). Clinical effects of infection with HBV range from headache, fever, malaise, nausea, vomiting, anorexia and abdominal pains. Replication of the virus is usually controlled by the immune response, with a course of recovery lasting weeks or months in humans, but infection may be more severe leading to persistent chronic liver disease. In "Viral Infections of Humans" (Second Edition, Ed., Evans, A. S. (1982) Plenum Publishing Corporation, New York), Chapter 12 describes in detail the etiology of viral hepatitis infections.